摘要:

Stratification of common ragweed (Ambrosia artemisiifolia)seeds at 4 C was most successful for breaking dormancy, whereas ‐5 C was least effective and 10 C was intermediate. Germination in the light exceeded that in the dark at all stratification and germination temperatures. The optimum temperatures for germination in the light were 10/20, 15/25, and 20/30. Maximum germination in the dark occurred at 20/30 C for seeds stratified at 4 and 10 C but the optimum temperatures for seeds stratified at ‐5 C were 10/20, 15/25, and 20/30. Seeds stratified at ‐5 and 10 C germinated best after 15 weeks of stratification, whereas 12 weeks of stratification at 4 C resulted in maximum germination. Secondary dormancy was induced in seeds which did not germinate in the dark. This was affected by stratification temperature and duration and germination temperature. The ecological significance of these germination characteristics is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb12333.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11755.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11756.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

In Onagraceae, pollen is shed in mature tetrads in most Epilobieae, many species ofLudwigia(Jussiaeeae), and two closely related species of the large genusCamissonia(Onagreae). Mature tetrads ofCamissonia cardiophyllaand representative species ofEpilobiumandLudwigiawere examined with light, scanning, and transmission electron microscopes. Morphological diagnoses of monad units indicated that individual taxa could be readily distinguished. Statistical analyses of tetrads which remained after acetolysis treatment revealed significant differences in the strength of the binding mechanisms. Mechanisms of tetrad cohesion were found to consist of two principal types. Common to all taxa is cohesion of pollen wall surfaces at the aperture margins; this mechanism is well known in many angiosperm groups. With the exception ofCamissonia, the remaining taxa also display binding by means of short exine fragments between adjacent pollen units. These fragments, termed bridges and reported here for the first time, are located in the area extending from the aperture margins to near the center of the proximal exine faces. Thin sections reveal that layers of the bridges are identical with those of the exine. Comparisons were made between bridges and viscin threads, both of which occur on the proximal faces of the grains. Viscin threads are present on all pollen grains in Onagraceae and exhibit distinctive morphologies, and bridges were viewed morphogenetically as related to viscin threads but including an endexine layer and occupying a position near the apertures where cohesion of wall surfaces also occurs. In an evolutionary sense, the formation of mature tetrads almost certainly occurred independently inCamissoniaand may have done so inLudwigiaand the Epilobieae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb12334.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11757.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11758.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11759.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11760.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Inclusions were found in epidermal plastids ofBeta vulgarisL., by the use of the electron microscope. One type of inclusion resembles the membrane‐bound plastid inclusions found by others in various meristematic plant cells; the other does not appear to have been described before. The second type of inclusion is not membrane‐bound and appears elongated and fibrillar in longisection. The elongated plastid inclusion sometimes becomes quite large. It is postulated thatBetaepidermal cells may store two different proteins under some conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb12335.x

出版商:Wiley    

年代:1975

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb11761.x

出版商:Wiley    

年代:1975

数据来源: WILEY